Abrasive particles and methods of making and using the same

ABSTRACT

Abrasive particles comprising ceramic (including glasses, crystalline ceramics, and glass-ceramics) comprising (on a theoretical oxide basis) Al 2 O 3  and at least one other metal oxide (e.g., REO and; REO and at least one of ZrO 2  or HfO 2 ) and methods of making the same. The abrasive particles can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.

[0001] This application is a continuation-in-part of U.S. Ser. No.09/922,528, filed Aug. 2, 2001, the disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

[0002] This invention relates to abrasive particles and methods ofmaking the same. The abrasive particles can be incorporated into avariety of abrasive articles, including bonded abrasives, coatedabrasives, nonwoven abrasives, and abrasive brushes.

DESCRIPTION OF RELATED ART

[0003] A large number of amorphous (including glass) and glass-ceramiccompositions are known. The majority of oxide glass systems utilizewell-known glass-formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃,and V₂O₅ to aid in the formation of the glass. Some of the glasscompositions formed with these glass-formers can be heat-treated to formglass-ceramics. The upper use temperature of glasses and glass-ceramicsformed from such glass formers is generally less than 1200° C.,typically about 700-800° C. The glass-ceramics tend to be moretemperature resistant than the glass from which they are formed.

[0004] In addition, many properties of known glasses and glass-ceramicsare limited by the intrinsic properties of glass-formers. For example,for SiO₂, B₂O₃, and P₂O₅-based glasses and glass-ceramics, the Young'smodulus, hardness, and strength are limited by such glass-formers. Suchglass and glass-ceramics generally have inferior mechanical propertiesas compared, for example, to Al₂O₃ or ZrO₂. Glass-ceramics having anymechanical properties similar to that of Al₂O₃ or ZrO₂ would bedesirable.

[0005] Although some non-conventional glasses such as glasses based onrare earth oxide-aluminum oxide (see, e.g., PCT application havingpublication No. WO 01/27046 A1, published Apr. 19, 2001, and JapaneseDocument No. JP 2000-045129, published Feb. 15, 2000) are known,additional novel glasses and glass-ceramic, as well as use for bothknown and novel glasses and glass-ceramics is desired.

[0006] In another aspect, a variety of abrasive particles (e.g., diamondparticles, cubic boron nitride particles, fused abrasive particles, andsintered, ceramic abrasive particles (including sol-gel-derived abrasiveparticles) known in the art. In some abrading applications, the abrasiveparticles are used in loose form, while in others the particles areincorporated into abrasive products (e.g., coated abrasive products,bonded abrasive products, non-woven abrasive products, and abrasivebrushes). Criteria used in selecting abrasive particles used for aparticular abrading application include: abrading life, rate of cut,substrate surface finish, grinding efficiency, and product cost.

[0007] From about 1900 to about the mid-1980's, the premier abrasiveparticles for abrading applications such as those utilizing coated andbonded abrasive products were typically fused abrasive particles. Thereare two general types of fused abrasive particles: (1) fused alphaalumina abrasive particles (see, e.g., U.S. Pat. Nos. 1,161,620(Coulter), 1,192,709 (Tone), 1,247,337 (Saunders et al.), 1,268,533(Allen), and 2,424,645 (Baumann et al.)) and (2) fused (sometimes alsoreferred to as “co-fused”) alumina-zirconia abrasive particles (see,e.g., U.S. Pat. Nos. 3,891,408 (Rowse et al.), 3,781,172 (Pett et al.),3,893,826 (Quinan et al.), 4,126,429 (Watson), 4,457,767 (Poon et al.),and 5,143,522 (Gibson et al.))(also see, e.g., U.S. Pat. Nos. 5,023,212(Dubots et. al) and 5,336,280 (Dubots et. al) which report the certainfused oxynitride abrasive particles). Fused alumina abrasive particlesare typically made by charging a furnace with an alumina source such asaluminum ore or bauxite, as well as other desired additives, heating thematerial above its melting point, cooling the melt to provide asolidified mass, crushing the solidified mass into particles, and thenscreening and grading the particles to provide the desired abrasiveparticle size distribution. Fused alumina-zirconia abrasive particlesare typically made in a similar manner, except the furnace is chargedwith both an alumina source and a zirconia source, and the melt is morerapidly cooled than the melt used to make fused alumina abrasiveparticles. For fused alumina-zirconia abrasive particles, the amount ofalumina source is typically about 50-80 percent by weight, and theamount of zirconia, 50-20 percent by weight zirconia. The processes formaking the fused alumina and fused alumina abrasive particles mayinclude removal of impurities from the melt prior to the cooling step.

[0008] Although fused alpha alumina abrasive particles and fusedalumina-zirconia abrasive particles are still widely used in abradingapplications (including those utilizing coated and bonded abrasiveproducts, the premier abrasive particles for many abrading applicationssince about the mid-1980's are sol-gel-derived alpha alumina particles(see, e.g., U.S. Pat. Nos. 4,314,827 (Leitheiser et al.), 4,518,397(Leitheiser et al.), 4,623,364 (Cottringer et al.), 4,744,802(Schwabel), 4,770,671 (Monroe et al.), 4,881,951 (Wood et al.),4,960,441 (Pellow et al.), 5,139,978 (Wood), 5,201,916 (Berg et al.),5,366,523 (Rowenhorst et al.), 5,429,647 (Larmie), 5,547,479 (Conwell etal.), 5,498,269 (Larmie), 5,551,963 (Larmie), and 5,725,162 (Garg etal.)).

[0009] The sol-gel-derived alpha alumina abrasive particles may have amicrostructure made up of very fine alpha alumina crystallites, with orwithout the presence of secondary phases added. The grinding performanceof the sol-gel derived abrasive particles on metal, as measured, forexample, by life of abrasive products made with the abrasive particleswas dramatically longer than such products made from conventional fusedalumina abrasive particles.

[0010] Typically, the processes for making sol-gel-derived abrasiveparticles are more complicated and expensive than the processes formaking conventional fused abrasive particles. In general,sol-gel-derived abrasive particles are typically made by preparing adispersion or sol comprising water, alumina monohydrate (boehmite), andoptionally peptizing agent (e.g., an acid such as nitric acid), gellingthe dispersion, drying the gelled dispersion, crushing the drieddispersion into particles, screening the particles to provide thedesired sized particles, calcining the particles to remove volatiles,sintering the calcined particles at a temperature below the meltingpoint of alumina, and screening and grading the particles to provide thedesired abrasive particle size distribution. Frequently a metal oxidemodifier(s) is incorporated into the sintered abrasive particles toalter or otherwise modify the physical properties and/or microstructureof the sintered abrasive particles.

[0011] There are a variety of abrasive products (also referred to“abrasive articles”) known in the art. Typically, abrasive productsinclude binder and abrasive particles secured within the abrasiveproduct by the binder. Examples of abrasive products include: coatedabrasive products, bonded abrasive products, nonwoven abrasive products,and abrasive brushes.

[0012] Examples of bonded abrasive products include: grinding wheels,cutoff wheels, and honing stones. The main types of bonding systems usedto make bonded abrasive products are: resinoid, vitrified, and metal.Resinoid bonded abrasives utilize an organic binder system (e.g.,phenolic binder systems) to bond the abrasive particles together to formthe shaped mass (see, e.g., U.S. Pat. Nos. 4,741,743 (Narayanan et al.),4,800,685 (Haynes et al.), 5,037,453 (Narayanan et al.), and 5,110,332(Narayanan et al.)). Another major type are vitrified wheels in which aglass binder system is used to bond the abrasive particles together mass(see, e.g., U.S. Pat. Nos. 4,543,107 (Rue), 4,898,587 (Hay et al.),4,997,461 (Markhoff-Matheny et al.), and 5,863,308 (Qi et al.)). Theseglass bonds are usually matured at temperatures between 900° C. to 1300°C. Today vitrified wheels utilize both fused alumina and sol-gel-derivedabrasive particles. However, fused alumina-zirconia is generally notincorporated into vitrified wheels due in part to the thermal stabilityof alumina-zirconia. At the elevated temperatures at which the glassbonds are matured, the physical properties of alumina-zirconia degrade,leading to a significant decrease in their abrading performance. Metalbonded abrasive products typically utilize sintered or plated metal tobond the abrasive particles.

[0013] The abrasive industry continues to desire abrasive particles andabrasive products that are easier to make, cheaper to make, and/orprovide performance advantage(s) over conventional abrasive particlesand products.

SUMMARY OF THE INVENTION

[0014] The present invention provides abrasive particles comprisingceramic (including amorphous materials, glasses, crystalline ceramics(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.REO)), and glass-ceramics) comprising (on a theoretical oxidebasis; e.g., may be present as a reaction product (e.g., CeAl₁₁O₁₈)),Al₂O₃ and at least one other metal oxide (e.g., REO and; REO and atleast one of ZrO₂ or HfO₂). In one aspect, abrasive particles accordingto the present invention typically have an average hardness (i.e.,resistance to deformation; also referred to as (“microhardness”);determined as described in the “Detailed Description (below) of atleast, 15 GPa, 16 GPa, 17 GPa, or even at least 18 GPa (or more). In oneaspect, the ceramic comprising the abrasive particles according to thepresent invention may comprise, for example, less than 40 (35, 30, 25,20, 15, 10, 5, 3, 2, 1, or even zero) percent by weight traditionalglass formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, and/or combinationsthereof, based on the total weight of the ceramic. In another aspect,the ceramic comprising the abrasive particles according to the presentinvention typically comprise, for example, zero, less than 25, 20, 15,10, 5, 4, 3, 2, or 1 percent by volume amorphous material. In anotheraspect, the ceramic comprising the abrasive particles according to thepresent invention typically comprise, for example, at least 75, 80, 85,90, 95, 97, 98, 99, or even 100 percent by volume crystalline ceramic.

[0015] Some embodiments desirably, the ceramic comprising the abrasiveparticles according to the present invention comprise at least 30 (moredesirably, in a range of about 30 to about 60) percent by weight of theAl₂O₃, based on the total weight of the ceramic. In another aspect, someembodiments desirably, the ceramic comprising the abrasive particlesaccording to the present invention comprise crystalline ceramic, whereinsome embodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers), and (b) is free of at least one of eutecticmicrostructure features (i.e., is free of colonies and lamellarstructure) or a non-cellular microstructure. It is also within the scopeof the present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

[0016] Some embodiments of abrasive particles according to the presentinvention comprise glass-ceramic comprising Al₂O₃ and at least one othermetal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂;),wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the glass-ceramic collectively comprises the Al₂O₃ and atleast one other metal oxide, based on the total weight of theglass-ceramic. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, or 95 percent by volume amorphous material. The glass-ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volumecrystalline ceramic.

[0017] Some embodiments of abrasive particles according to the presentinvention comprise glass-ceramic comprising Al₂O₃ and at least one othermetal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the glass-ceramic collectively comprises theAl₂O₃ and at least one other metal oxide, and less than 20 (preferably,less than 15, 10, 5, or even 0) percent by weight SiO₂, and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight B₂O₃,based on the total weight of the glass-ceramic. The glass-ceramic maycomprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volumeamorphous material. The glass-ceramic may comprise, for example, atleast 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35,30, 25, 20, 15, 10, or 5 percent by volume crystalline ceramic.

[0018] Some embodiments of abrasive particles according to the presentinvention comprise glass-ceramic comprising Al₂O₃ and at least one othermetal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the glass-ceramic collectively comprises theAl₂O₃ and at least one other metal oxide, and less than 40 percent(preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0) by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass-ceramic. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, percent by volume amorphous material. The glass-ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volumecrystalline ceramic.

[0019] Some embodiments of abrasive particles according to the presentinvention comprise glass-ceramic comprising Al₂O₃ and at least one othermetal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.REO)) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300or 150 nanometers; and in some embodiments, less than 20 nanometers),and (b) is free of eutectic microstructure features. Some embodiments ofabrasive particles according to the present invention compriseglass-ceramic comprising Al₂O₃ and at least one other metal oxide (e.g.,REO and; REO and at least one of ZrO₂ or HfO₂), wherein theglass-ceramic (a) exhibits a non-cellular microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.REO)) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, even less than 300 or150 nanometers; and in some embodiments, less than 20 nanometers). Theglass-ceramic may comprise, for example, at least 1, 2, 3, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, percentby volume amorphous material. The glass-ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volume crystallineceramic. It is also within the scope of the present invention for someembodiments to have at least one crystalline phase within a specifiedaverage crystallite value and at least one (different) crystalline phaseoutside of a specified average crystallite value.

[0020] Some embodiments of abrasive particles according to the presentinvention comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising Al₂O₃ and atleast one other metal oxide (e.g., REO and; REO and at least one of ZrO₂or HfO₂), wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100)percent by weight of the crystalline ceramic collectively comprises theAl₂O₃ and at least one other metal oxide, based on the total weight ofthe crystalline ceramic. Some desirable embodiments include thosewherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.REO)) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300or 150 nanometers; and in some embodiments, less than 20 nanometers),and (b) is free of eutectic microstructure features. Some embodiments ofabrasive particles according to the present invention include thosewherein the ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)) having an average crystallite size of lessthan 1 micrometer (typically, less than 500 nanometers, even less than300 or 150 nanometers; and in some embodiments, less than 20nanometers). The ceramic may comprise, for example, at least 99, 98, 97,95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10,5, 3, 2, or 1 percent by volume amorphous material. It is also withinthe scope of the present invention for some embodiments to have at leastone crystalline phase within a specified average crystallite value andat least one (different) crystalline phase outside of a specifiedaverage crystallite value.

[0021] Some embodiments of abrasive particles according to the presentinvention comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising Al₂O₃ and atleast one other metal oxide (e.g., REO and; REO and at least one of ZrO₂or HfO₂), wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100) percent by weight of the crystalline ceramic collectivelycomprises the Al₂O₃ and at least one other metal oxide, and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight SiO₂, andless than 20 (preferably, less than 15, 10, 5, or even 0) percent byweight B₂O₃, based on the total weight of the crystalline ceramic. Somedesirable embodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers, oreven less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers), and (b) is free of eutectic microstructure features.Some embodiments of abrasive particles according to the presentinvention include those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers). The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume amorphous material. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified average crystallitevalue and at least one (different) crystalline phase outside of aspecified average crystallite value.

[0022] Some embodiments of abrasive particles according to the presentinvention comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the crystalline ceramic comprising Al₂O₃ and atleast one other metal oxide (e.g., REO and; REO and at least one of ZrO₂or HfO₂), wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100) percent by weight of the crystalline ceramic collectivelycomprises the Al₂O₃ and at least one other metal oxide, and less than 40(preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0) percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe crystalline ceramic. Some desirable embodiments include thosewherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.REO)) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than lessthan 300 or 150 nanometers; and in some embodiments, less than 20nanometers), and (b) is free of eutectic microstructure features. Someembodiments of abrasive particles according to the present inventioninclude those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers). The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume amorphous material. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified average crystallitevalue and at least one (different) crystalline phase outside of aspecified average crystallite value.

[0023] Some embodiments of abrasive particles according to the presentinvention comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising Al₂O₃ and at least oneother metal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂).Desirable some embodiments include those wherein the ceramic (a)exhibits a microstructure comprising crystallites (e.g., crystallites ofa complex metal oxide(s) (e.g., complex Al₂O₃.REO)) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300 or 150 nanometers; and in someembodiments, less than 20 nanometers), and (b) is free of eutecticmicrostructure features. Some embodiments of abrasive particlesaccording to the present invention include those wherein the ceramic (a)exhibits a non-cellular microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃.REO))having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300 or 150 nanometers; and insome embodiments, less than 20 nanometers). The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeamorphous material. It is also within the scope of the present inventionfor some embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

[0024] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising Al₂O₃ and at least oneother metal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the ceramic collectively comprises the Al₂O₃ and at least oneother metal oxide, based on the total weight of the ceramic. Somedesirable embodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers, oreven less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers), and (b) is free of eutectic microstructure features.Some embodiments of abrasive particles according to the presentinvention include those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers). The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume amorphous material. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified average crystallitevalue and at least one (different) crystalline phase outside of aspecified average crystallite value.

[0025] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising Al₂O₃ and at least oneother metal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the ceramic collectively comprises the Al₂O₃and at least one other metal oxide, and less than 20 (preferably, lessthan 15, 10, 5, or even 0) percent by weight SiO₂ and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight B₂O₃,based on the total weight of the ceramic. Some desirable embodimentsinclude those wherein the ceramic (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)) having an average crystallite size of lessthan 1 micrometer (typically, less than 500 nanometers, or even lessthan 300 or 150 nanometers; and in some embodiments, less than 20nanometers), and (b) is free of eutectic microstructure features. Someembodiments of abrasive particles according to the present inventioninclude those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.REO)) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300 or 150 nanometers; and in some embodiments, less than20 nanometers). The ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, 5, 3, 2, or 1 percent by volume amorphous material. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified average crystallitevalue and at least one (different) crystalline phase outside of aspecified average crystallite value.

[0026] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic (e.g., atleast 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystalline ceramic), the ceramic comprising Al₂O₃ and at least oneother metal oxide (e.g., REO and; REO and at least one of ZrO₂ or HfO₂),wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the ceramic collectively comprises the Al₂O₃and at least one other metal oxide, and less than 40 (preferably, lessthan 35, 30, 25, 20, 15, 10, 5, or even 0) percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theceramic. Desirable some embodiments include those wherein the ceramic(a) exhibits a microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃.REO))having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, or even less than 300 or 150 nanometers; andin some embodiments, less than 20 nanometers), and (b) is free ofeutectic microstructure features. Some embodiments of abrasive particlesaccording to the present invention include those wherein the ceramic (a)exhibits a non-cellular microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃.REO))having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300 or 150 nanometers; and insome embodiments, less than 20 nanometers). The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeamorphous material. It is also within the scope of the present inventionfor some embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

[0027] Some embodiments of abrasive particles according to the presentinvention may comprise glass-ceramic comprising Al₂O₃ and REO, whereinthe glass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.REO)) having an average crystallite size of less than 200nanometers (150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) and (b) has a density of at least 90% (95%, 96%, 97%, 98%,99%, 99.5%, or 100%) of theoretical density. Some embodiments can befree of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

[0028] Some embodiments of abrasive particles according to the presentinvention may comprise glass-ceramic comprising Al₂O₃ and REO, whereinthe glass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.REO)), wherein none of the crystallites are greater than 200nanometers (150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0029] Some embodiments of abrasive particles according to the presentinvention may comprise glass-ceramic comprising Al₂O₃ and REO, whereinthe glass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.REO)), wherein at least a portion of the crystallites are notgreater than 150 nanometers (100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0030] Some embodiments of abrasive particles according to the presentinvention may comprise fully crystallized glass-ceramic comprising Al₂O₃and REO, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)) having an average crystallite size notgreater than 1 micrometer (500 nanometers, 300 nanometers, 200nanometers, 150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0031] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic, whereinthe ceramic comprises Al₂O₃ and REO, and (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)) having an average crystallite size of lessthan 200 nanometers (150 nanometers, 100 nanometers, or even 50nanometers) and (b) has a density of at least 90% (95%, 96%, 97%, 98%,99%, 99.5%, or 100%) of theoretical density. Some embodiments can befree of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

[0032] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic, whereinthe ceramic comprises Al₂O₃ and REO, and (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)), wherein none of the crystallites are greaterthan 200 nanometers (150 nanometers, 100 nanometers, 75 nanometers, oreven 50 nanometers) in size and (b) has a density of at least 90% (95%,96%, 97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Someembodiments can be free of at least one of eutectic microstructurefeatures or a non-cellular microstructure. It is also within the scopeof the present invention for some embodiments to have at least onecrystalline phase within a specified crystallite value and at least one(different) crystalline phase outside of a specified crystallite value.

[0033] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic, whereinthe ceramic comprises Al₂O₃ and REO, and (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)), wherein at least a portion of thecrystallites are not greater than 150 nanometers (100 nanometers, 75nanometers, or even 50 nanometers) in size and (b) has a density of atleast 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) of theoreticaldensity. Some embodiments can be free of at least one of eutecticmicrostructure features or a non-cellular microstructure. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified crystallite value andat least one (different) crystalline phase outside of a specifiedcrystallite value.

[0034] Some embodiments of abrasive particles according to the presentinvention may comprise ceramic comprising crystalline ceramic, whereinthe ceramic comprises Al₂O₃ and REO, and (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.REO)) having an average crystallite size notgreater than 1 micrometer (500 nanometers, 300 nanometers, 200nanometers, 150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified crystallite value and at least one (different)crystalline phase outside of a specified crystallite value.

[0035] In this application:

[0036] “amorphous material” refers to material derived from a meltand/or a vapor phase that lacks any long range crystal structure asdetermined by X-ray diffraction and/or has an exothermic peakcorresponding to the crystallization of the amorphous material asdetermined by a DTA (differential thermal analysis) as determined by thetest described herein entitled “Differential Thermal Analysis”;

[0037] “ceramic” includes amorphous material, glass, crystallineceramic, glass-ceramic, and combinations thereof;

[0038] “complex metal oxide” refers to a metal oxide comprising two ormore different metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgAl₂O₄, and Y₃Al₅O₁₂);

[0039] “complex Al₂O₃.metal oxide” refers to a complex metal oxidecomprising, on a theoretical oxide basis, Al₂O₃ and one or more metalelements other than Al (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂, MgAl₂O₄, andY₃Al₅O₁₂);

[0040] “complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

[0041] “complex Al₂O₃.REO” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and rare earth oxide (e.g.,CeAl₁₁O₁₈ and Dy₃Al₅O₁₂);

[0042] “glass” refers to amorphous material exhibiting a glasstransition temperature;

[0043] “glass-ceramic” refers to ceramics comprising crystals formed byheat-treating amorphous material;

[0044] “T_(g)” refers to the glass transition temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0045] “T_(x)” refers to the crystallization temperature as determinedby the test described herein entitled “Differential Thermal Analysis”;

[0046] “rare earth oxides” refers to cerium oxide (e.g., CeO₂),dysprosium oxide (e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europiumoxide (e.g., Eu₂O₃), gadolinium (e.g., Gd₂O₃), holmium oxide (e.g.,Ho₂O₃), lanthanum oxide (e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃),neodymium oxide (e.g., Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁),samarium oxide (e.g., Sm₂O₃), terbium (e.g., Tb₂O₃), thorium oxide(e.g., Th₄O₇), thulium (e.g., Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃),and combinations thereof;

[0047] “REO” refers to rare earth oxide(s).

[0048] Further, it is understood herein that unless it is stated that ametal oxide (e.g., Al₂O₃, complex Al₂O₃.metal oxide, etc.) iscrystalline, for example, in a glass-ceramic, it may be amorphous,crystalline, or portions amorphous and portions crystalline. For exampleif a glass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may eachbe in an amorphous state, crystalline state, or portions in an amorphousstate and portions in a crystalline state, or even as a reaction productwith another metal oxide(s) (e.g., unless it is stated that, forexample, Al₂O₃ is present as crystalline Al₂O₃ or a specific crystallinephase of Al₂O₃ (e.g., alpha Al₂O₃), it may be present as crystallineAl₂O₃ and/or as part of one or more crystalline complex Al₂O₃.metaloxides.

[0049] Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

[0050] Abrasive articles according to the present invention comprisebinder and a plurality of abrasive particles, wherein at least a portionof the abrasive particles are the abrasive particles according to thepresent invention. Exemplary abrasive products include coated abrasivearticles, bonded abrasive articles (e.g., wheels), non-woven abrasivearticles, and abrasive brushes. Coated abrasive articles typicallycomprise a backing having first and second, opposed major surfaces, andwherein the binder and the plurality of abrasive particles form anabrasive layer on at least a portion of the first major surface.

[0051] In some embodiments, preferably, at least 5, 10, 15, 20, 25, 30,35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percentby weight of the abrasive particles in an abrasive article are theabrasive particles according to the present invention, based on thetotal weight of the abrasive particles in the abrasive article.

[0052] Abrasive particles are usually graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards (i.e., specified nominal grades) include those knownas the American National Standards Institute, Inc. (ANSI) standards,Federation of European Producers of Abrasive Products (FEPA) standards,and Japanese Industrial Standard (JIS) standards. In one aspect, thepresent invention provides a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles are abrasive particles according to the presentinvention. In some embodiments, preferably, at least 5, 10, 15, 20, 25,30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100percent by weight of the plurality of abrasive particles are theabrasive particles according to the present invention, based on thetotal weight of the plurality of abrasive particles.

[0053] Abrasive particles according to the present invention can beincorporated into various abrasive products such as coated abrasives,bonded abrasives, nonwoven abrasives, and abrasive brushes, as well asbe used in loose form.

[0054] The present invention also provides a method of abrading asurface, the method comprising:

[0055] contacting abrasive particles according to the present inventionwith a surface of a workpiece; and

[0056] moving at least one of the abrasive particles according to thepresent invention or the contacted surface to abrade at least a portionof the surface with at least one of the abrasive particles according tothe present invention.

BRIEF DESCRIPTION OF THE DRAWING

[0057]FIG. 1 is a fragmentary cross-sectional schematic view of a coatedabrasive article including abrasive particles according to the presentinvention;

[0058]FIG. 2 is a perspective view of a bonded abrasive articleincluding abrasive particles according to the present invention;

[0059]FIG. 3 is an enlarged schematic view of a nonwoven abrasivearticle including abrasive particles according to the present invention;

[0060]FIG. 4 is a DTA curve of Example 1 material; and

[0061] FIGS. 5-8 is an SEM micrograph of Example 2, 6, 7, 8, 17,respectively, material heat-treated at 1300° C. for 1 hour.

DETAILED DESCRIPTION

[0062] Abrasive particles according to the present invention can be madeby crystallizing amorphous material or ceramic comprising amorphousmaterial to form glass-ceramic. In one aspect, amorphous materials formaking abrasive particles according to the present invention includethose comprising Al₂O₃, and at least one other metal oxide (e.g., REOand; REO and at least one of ZrO₂ or HfO₂), wherein at least 80 (85, 90,95, 97, 98, 99, or even 100) percent by weight of the amorphous materialcollectively comprises the comprises the Al₂O₃, and at least one othermetal oxide, based on the total weight of the amorphous material.

[0063] In another aspect, amorphous materials for making abrasiveparticles according to the present invention include those comprisingAl₂O₃, and at least one other metal oxide (e.g., REO and; REO and atleast one of ZrO₂ or HfO₂), wherein at least 60 (65, 70, 75, 80, 85, 90,95, 97, 98, 99, or even 100) percent by weight of the amorphous materialcollectively comprises the Al₂O₃, and at least one other metal oxide,and less than 20 (preferably, less than 15, 10, 5, or even 0) percent byweight SiO₂ and less than 20 (preferably, less than 15, 10, 5, or even0) percent by weight B₂O₃, based on the total weight of the amorphousmaterial.

[0064] In another aspect, amorphous materials for making abrasiveparticles according to the present invention include those comprisingAl₂O₃, and at least one other metal oxide (e.g., REO and; REO and atleast one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75, 80, 85, 90,95, 97, 98, 99, or even 100) percent by weight of the amorphous materialcollectively comprises the Al₂O₃, and at least one other metal oxide,and less than 40 (preferably, less than 35, 30, 25, 20, 15, 10, 5, oreven 0) percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the amorphous material.

[0065] Amorphous materials or ceramic comprising amorphous material canbe made by heating (including in a flame) the appropriate metal oxidesources to form a melt, desirably a homogenous melt, and then rapidlycooling the melt to provide amorphous material. For example, amorphousmaterials can be made, for example, by heating (including in a flame)the appropriate metal oxide sources to form a melt, desirably ahomogenous melt, and then rapidly cooling the melt to provide amorphousmaterial. Some embodiments of amorphous materials can be made, forexample, by melting the metal oxide sources in any suitable furnace(e.g., an inductive heated furnace, a gas-fired furnace, or anelectrical furnace), or, for example, in a plasma. The resulting melt iscooled (e.g., discharging the melt into a cooling media (e.g., highvelocity air jets, liquids, metal plates (including chilled metalplates), metal rolls (including chilled metal rolls), metal balls(including chilled metal balls), and the like)). In one method,amorphous materials and ceramic comprising amorphous materials can bemade utilizing flame fusion as disclosed, for example, in U.S. Pat. No.6,254,981 (Castle), the disclosure of which is incorporated herein byreference. In this method, the metal oxide sources materials are fed(e.g., in the form of particles, sometimes referred to as “feedparticles”) directly into a burner (e.g., a methane-air burner, anacetylene-oxygen burner, a hydrogen-oxygen burner, and like), and thenquenched, for example, in water, cooling oil, air, or the like. Feedparticles can be formed, for example, by grinding, agglomerating (e.g.,spray-drying), melting, or sintering the metal oxide sources. The sizeof feed particles fed into the flame generally determine the size of theresulting amorphous material comprising particles.

[0066] Some embodiments of amorphous materials can also be obtained byother techniques, such as: laser spin melt with free fall cooling,Taylor wire technique, plasmatron technique, hammer and anvil technique,centrifugal quenching, air gun splat cooling, single roller and twinroller quenching, roller-plate quenching and pendant drop meltextraction (see, e.g., Rapid Solidification of Ceramics, Brockway et.al, Metals And Ceramics Information Center, A Department of DefenseInformation Analysis Center, Columbus, Ohio, January, 1984, thedisclosure of which is incorporated here as a reference). Someembodiments of amorphous materials may also be obtained by othertechniques, such as: thermal (including flame or laser orplasma-assisted) pyrolysis of suitable precursors, physical vaporsynthesis (PVS) of metal precursors and mechanochemical processing.

[0067] Useful amorphous material formulations include those at or near aeutectic composition(s) (e.g., binary and ternary eutecticcompositions). In addition to compositions disclosed herein, othercompositions, including quaternary and other higher order eutecticcompositions, may be apparent to those skilled in the art afterreviewing the present disclosure.

[0068] Sources, including commercial sources, of (on a theoretical oxidebasis) Al₂O₃ include bauxite (including both natural occurring bauxiteand synthetically produced bauxite), calcined bauxite, hydrated aluminas(e.g., boehmite, and gibbsite), aluminum, Bayer process alumina,aluminum ore, gamma alumina, alpha alumina, aluminum salts, aluminumnitrates, and combinations thereof. The Al₂O₃ source may contain, oronly provide, Al₂O₃. Alternatively, the Al₂O₃ source may contain, orprovide Al₂O₃, as well as one or more metal oxides other than Al₂O₃(including materials of or containing complex Al₂O₃.metal oxides (e.g.,Dy₃Al₅O₁₂, Y₃Al₅O₁₂, CeAl₁₁ O₁₈, etc.)).

[0069] Sources, including commercial sources, of rare earth oxidesinclude rare earth oxide powders, rare earth metals, rareearth-containing ores (e.g., bastnasite and monazite), rare earth salts,rare earth nitrates, and rare earth carbonates. The rare earth oxide(s)source may contain, or only provide, rare earth oxide(s). Alternatively,the rare earth oxide(s) source may contain, or provide rare earthoxide(s), as well as one or more metal oxides other than rare earthoxide(s) (including materials of or containing complex rare earthoxide.other metal oxides (e.g., Dy₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

[0070] Sources, including commercial sources, of (on a theoretical oxidebasis) Y₂O₃ include yttrium oxide powders, yttrium, yttrium-containingores, and yttrium salts (e.g., yttrium carbonates, nitrates, chlorides,hydroxides, and combinations thereof). The Y₂O₃ source may contain, oronly provide, Y₂O₃. Alternatively, the Y₂O₃ source may contain, orprovide Y₂O₃, as well as one or more metal oxides other than Y₂O₃(including materials of or containing complex Y₂O₃.metal oxides (e.g.,Y₃Al₅O₁₂)).

[0071] Sources, including commercial sources, of (on a theoretical oxidebasis) ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

[0072] Other useful metal oxide may also include, on a theoretical oxidebasis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO, NiO, Na₂O,P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, ZnO, and combinations thereof.Sources, including commercial sources, include the oxides themselves,complex oxides, ores, carbonates, acetates, nitrates, chlorides,hydroxides, etc.

[0073] In some embodiments, it may be advantageous for at least aportion of a metal oxide source (in some embodiments, preferably, 10 15,20, 25, 30, 35, 40, 45,, or even at least 50 percent by weight) to beobtained by adding particulate, metallic material comprising at leastone of a metal (e.g., Al, Ca, Cu, Cr, Fe, Li, Mg, Ni, Ag, Ti, Zr, andcombinations thereof), M, that has a negative enthalpy of oxideformation or an alloy thereof to the melt, or otherwise metal them withthe other raw materials. Although not wanting to be bound by theory, itis believed that the heat resulting from the exothermic reactionassociated with the oxidation of the metal is beneficial in theformation of a homogeneous melt and resulting amorphous material. Forexample, it is believed that the additional heat generated by theoxidation reaction within the raw material eliminates or minimizesinsufficient heat transfer, and hence facilitates formation andhomogeneity of the melt, particularly when forming amorphous particleswith x, y, and z dimensions over 150 micrometers. It is also believedthat the availability of the additional heat aids in driving variouschemical reactions and physical processes (e.g., densification, andspherodization) to completion. Further, it is believed for someembodiments, the presence of the additional heat generated by theoxidation reaction actually enables the formation of a melt, whichotherwise is difficult or otherwise not practical due to high meltingpoint of the materials. Further, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation ofamorphous material that otherwise could not be made, or could not bemade in the desired size range. Another advantage of the inventioninclude, in forming the amorphous materials, that many of the chemicaland physical processes such as melting, densification and spherodizingcan be achieved in a short time, so that very high quench rates be canachieved. For additional details, see copending application having U.S.Ser. No. ______ (Attorney Docket No. 56931US007), filed the same date asthe instant application, the disclosure of which is incorporated hereinby reference.

[0074] The addition of certain metal oxides may alter the propertiesand/or crystalline structure or microstructure of ceramic comprisingabrasive particles according to the present invention, as well as theprocessing of the raw materials and intermediates in making the ceramic.For example, oxide additions such as MgO, CaO, Li₂O, and Na₂O have beenobserved to alter both the T_(g) and T_(x) (wherein T_(x) is thecrystallization temperature) of glass. Although not wishing to be boundby theory, it is believed that such additions influence glass formation.Further, for example, such oxide additions may decrease the meltingtemperature of the overall system (i.e., drive the system toward lowermelting eutectic), and ease of glass-formation. Complex eutectics inmulti component systems (quaternary, etc.) may result in betterglass-forming ability. The viscosity of the liquid melt and viscosity ofthe glass in its' “working” range may also be affected by the additionof certain metal oxides such as MgO, CaO, Li₂O, and Na₂O.

[0075] Typically, amorphous materials and the glass-ceramics accordingto the present invention have x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 10 micrometers. In some embodiments, the x, y, and z dimensions isat least 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers,50 micrometers, 75 micrometers, 100 micrometers, 150 micrometers, 200micrometers, 250 micrometers, 500 micrometers, 1000 micrometers, 2000micrometers, 2500 micrometers, 1 mm, 5 mm, or even at least 10 mm. Thex, y, and z dimensions of a material are determined either visually orusing microscopy, depending on the magnitude of the dimensions. Thereported z dimension is, for example, the diameter of a sphere, thethickness of a coating, or the longest length of a prismatic shape.

[0076] Crystallization of amorphous material and ceramic comprising theamorphous may also be affected by the additions of certain materials.For example, certain metals, metal oxides (e.g., titanates andzirconates), and fluorides, for example, may act as nucleation agentsresulting in beneficial heterogeneous nucleation of crystals. Also,addition of some oxides may change nature of metastable phasesdevitrifying from the amorphous material upon reheating. In anotheraspect, for ceramics comprising crystalline ZrO₂, it may be desirable toadd metal oxides (e.g., Y₂O₃, TiO₂, CaO, and MgO) that are known tostabilize tetragonal/cubic form of ZrO₂.

[0077] The particular selection of metal oxide sources and otheradditives for making ceramics according to the present inventiontypically takes into account, for example, the desired composition andmicrostructure of the resulting crystalline containing ceramics, thedesired degree of crystallinity, if any, the desired physical properties(e.g., hardness or toughness) of the resulting ceramics, avoiding orminimizing the presence of undesirable impurities, the desiredcharacteristics of the resulting ceramics, and/or the particular process(including equipment and any purification of the raw materials beforeand/or during fusion and/or solidification) being used to prepare theceramics.

[0078] In some instances, it may be preferred to incorporate limitedamounts of metal oxides selected from the group consisting of: Na₂O,P₂O₅, SiO₂, TeO₂, V₂O₃, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting abrasive particles and/or improve processing. These metaloxides when used are typically are added from greater than 0 to 20% byweight, preferably greater than 0 to 5% by weight and more preferablygreater than 0 to 2% by weight of the glass-ceramic depending, forexample, upon the desired property.

[0079] The metal oxide sources and other additives can be in any formsuitable to the process and equipment being used to make the ceramiccomprising abrasive particles according to the present invention. Theraw materials can be melted and quenched using techniques and equipmentknown in the art for making oxide glasses and amorphous metals.Desirable cooling rates include those of 50K/s and greater. Coolingtechniques known in the art include roll-chilling. Roll-chilling can becarried out, for example, by melting the metal oxide sources at atemperature typically 20-200° C. higher than the melting point, andcooling/quenching the melt by spraying it under high pressure (e.g.,using a gas such as air, argon, nitrogen or the like) onto a high-speedrotary roll(s). Typically, the rolls are made of metal and are watercooled. Metal book molds may also be useful for cooling/quenching themelt.

[0080] Other techniques for forming melts, cooling/quenching melts,and/or otherwise forming amorphous materials include vapor phasequenching, plasma spraying, melt-extraction, and gas or centrifugalatomization. Vapor phase quenching can be carried out, for example, bysputtering, wherein the metal alloys or metal oxide sources are formedinto a sputtering target(s) which are used. The target is fixed at apredetermined position in a sputtering apparatus, and a substrate(s) tobe coated is placed at a position opposing the target(s). Typicalpressures of 10⁻³ torr of oxygen gas and Ar gas, discharge is generatedbetween the target(s) and a substrate(s), and Ar or oxygen ions collideagainst the target to start reaction sputtering, thereby depositing afilm of composition on the substrate. For additional details regardingplasma spraying, see, for example, copending application having U.S.Ser. No. ______ (Attorney Docket No. 57980US002), filed the same date asthe instant application, the disclosure of which is incorporated hereinby reference.

[0081] Gas atomization involves melting feed particles to convert themto melt. A thin stream of such melt is atomized through contact with adisruptive air jet (i.e., the stream is divided into fine droplets). Theresulting substantially discrete, generally ellipsoidal glass particles(e.g., beads) are then recovered. Examples of bead sizes include thosehaving a diameter in a range of about 5 micrometers to about 3 mm.Melt-extraction can be carried out, for example, as disclosed in U.S.Pat. No. 5,605,870 (Strom-Olsen et al.), the disclosure of which isincorporated herein by reference. Containerless glass forming techniquesutilizing laser beam heating as disclosed, for example, in PCTapplication having Publication No. WO 01/27046 A1, published Apr. 4,2001, the disclosure of which is incorporated herein by reference, mayalso be useful in making glass according to the present invention.

[0082] The cooling rate is believed to affect the properties of thequenched amorphous material. For instance, glass transition temperature,density and other properties of glass typically change with coolingrates.

[0083] Rapid cooling may also be conducted under controlled atmospheres,such as a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence glass formation by influencingcrystallization kinetics from undercooled liquid. For example, largerundercooling of Al₂O₃ melts without crystallization has been reported inargon atmosphere as compared to that in air.

[0084] The microstructure or phase composition(glassy/amorphous/crystalline) of a material can be determined in anumber of ways. Various information can be obtained using opticalmicroscopy, electron microscopy, differential thermal analysis (DTA),and x-ray diffraction (XRD), for example.

[0085] Using optical microscopy, amorphous material is typicallypredominantly transparent due to the lack of light scattering centerssuch as crystal boundaries, while crystalline material shows acrystalline structure and is opaque due to light scattering effects.

[0086] A percent amorphous yield can be calculated for beads using a−100+120 mesh size fraction (i.e., the fraction collected between150-micrometer opening size and 125-micrometer opening size screens).The measurements are done in the following manner. A single layer ofbeads is spread out upon a glass slide. The beads are observed using anoptical microscope. Using the crosshairs in the optical microscopeeyepiece as a guide, beads that lay along a straight line are countedeither amorphous or crystalline depending on their optical clarity. Atotal of 500 beads are counted and a percent amorphous yield isdetermined by the amount of amorphous beads divided by total beadscounted.

[0087] Using DTA, the material is classified as amorphous if thecorresponding DTA trace of the material contains an exothermiccrystallization event (T_(x)). If the same trace also contains anendothermic event (T_(g)) at a temperature lower than T_(x) it isconsidered to consist of a glass phase. If the DTA trace of the materialcontains no such events, it is considered to contain crystalline phases.

[0088] Differential thermal analysis (DTA) can be conducted using thefollowing method. DTA runs can be made (using an instrument such as thatobtained from Netzsch Instruments, Selb, Germany under the tradedesignation “NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh sizefraction (i.e., the fraction collected between 105-micrometer openingsize and 90-micrometer opening size screens). An amount of each screenedsample (typically about 400 milligrams (mg)) is placed in a100-microliter Al₂O₃ sample holder. Each sample is heated in static airat a rate of 10° C./minute from room temperature (about 25° C.) to 1100°C.

[0089] Using powder x-ray diffraction, XRD, (using an x-raydiffractometer such as that obtained under the trade designation“PHILLIPS XRG 3100” from Phillips, Mahwah, N.J., with copper K α1radiation of 1.54050 Angstrom) the phases present in a material can bedetermined by comparing the peaks present in the XRD trace of thecrystallized material to XRD patterns of crystalline phases provided inJCPDS (Joint Committee on Powder Diffraction Standards) databases,published by International Center for Diffraction Data. Furthermore, anXRD can be used qualitatively to determine types of phases. The presenceof a broad diffused intensity peak is taken as an indication of theamorphous nature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix. The initially formed amorphousmaterial or ceramic (including glass prior to crystallization) may belarger in size than that desired. The amorphous material or ceramic canbe converted into smaller pieces using crushing and/or comminutingtechniques known in the art, including roll crushing, canary milling,jaw crushing, hammer milling, ball milling, jet milling, impactcrushing, and the like. In some instances, it is desired to have two ormultiple crushing steps. For example, after the ceramic is formed(solidified), it may be in the form of larger than desired. The firstcrushing step may involve crushing these relatively large masses or“chunks” to form smaller pieces. This crushing of these chunks may beaccomplished with a hammer mill, impact crusher or jaw crusher. Thesesmaller pieces may then be subsequently crushed to produce the desiredparticle size distribution. In order to produce the desired particlesize distribution (sometimes referred to as grit size or grade), it maybe necessary to perform multiple crushing steps. In general the crushingconditions are optimized to achieve the desired particle shape(s) andparticle size distribution. Resulting particles that are of the desiredsize may be recrushed if they are too large, or “recycled” and used as araw material for re-melting if they are too small.

[0090] The shape of abrasive particles can depend, for example, on thecomposition and/or microstructure of the ceramic, the geometry in whichit was cooled, and the manner in which the ceramic is crushed (i.e., thecrushing technique used). In general, where a “blocky” shape ispreferred, more energy may be employed to achieve this shape.Conversely, where a “sharp” shape is preferred, less energy may beemployed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. For some particles anaverage aspect ratio ranging from 1:1 to 5:1 is typically desired, andin some embodiments 1.25:1 to 3:1, or even 1.5:1 to 2.5:1.

[0091] It is also within the scope of the present invention, forexample, to directly form abrasive particles in desired shapes. Forexample, abrasive particles may be formed (including molded) by pouringor forming the melt into a mold.

[0092] It is also within the scope of the present invention, forexample, to fabricate the ceramic (including glass prior tocrystallization) by coalescing. This coalescing step in essence forms alarger sized body from two or more smaller particles. For example,amorphous material comprising particles (obtained, for example, bycrushing) (including beads and microspheres), fibers, etc. may formedinto a larger particle size. For example, ceramic (including glass priorto crystallization), may also be provided by heating, for example,particles comprising the amorphous material, and/or fibers, etc. abovethe T_(g) such that the particles, etc. coalesce to form a shape andcooling the coalesced shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the amorphousmaterial and the desired density of the resulting material. Thetemperature should below glass crystallization temperature, and forglasses, greater than the glass transition temperature. In certainembodiments, the heating is conducted at at least one temperature in arange of about 850° C. to about 1100° C. (in some embodiments,preferably 900° C. to 1000° C.). Typically, the amorphous material isunder pressure (e.g., greater than zero to 1 GPa or more) duringcoalescence to aid the coalescence of the amorphous material. In oneembodiment, a charge of the particles, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into a relatively large part.Examples of typical coalescing techniques include hot pressing, hotisostatic pressure, hot extrusion and the like. Typically, it isgenerally preferred to cool the resulting coalesced body before furtherheat treatment. After heat treatment if so desired, the coalesced bodymay be crushed to smaller particle sizes or a desired particle sizedistribution.

[0093] Glass forms for making abrasive particles according to thepresent invention, may also be provided by heating, for example, glassor particles comprising glass (including beads, microspheres, and powder(obtained, for example, by crushing) and fibers, etc.) above the T_(g)such that the particles comprising glass, etc. coalesce to form a shapeand cooling the coalesced shape. In certain embodiments, the heating isconducted at at least one temperature in a range of about 850° C. toabout 1100° C. Typically, the glass is under pressure during coalescenceto aid the coalescence of the glass. In one embodiment, a charge of theglass particles, etc. is placed into a die and hot-pressing is performedat temperatures above glass transition where viscous flow of glass leadsto coalescence into a relatively large part. It is also within the scopeof the present invention to conduct additional heat-treatment to furtherimprove desirable properties of the material. For example, hot-isostaticpressing may be conducted (e.g., at temperatures from about 900° C. toabout 1400° C.) to remove residual porosity, increasing the density ofthe material. It is also within the scope of the present invention tocoalesce glass particles, etc. may be conducted via hot-isostaticpressing. Optionally, the resulting, coalesced article can beheat-treated to provide glass-ceramic, crystalline ceramic, or ceramicotherwise comprising crystalline ceramic.

[0094] It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 900° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. Optionally, theresulting, coalesced article can be heat-treated to provideglass-ceramic, crystalline ceramic, or ceramic otherwise comprisingcrystalline ceramic.

[0095] Coalescing of the amorphous material and/or glass-ceramic (e.g.,particles) may also be accomplished by a variety of methods, includingpressureless or pressure sintering (e.g., sintering, plasma assistedsintering, hot pressing, IIIPing, hot forging, hot extrusion, etc.).

[0096] Heat-treatment can be carried out in any of a variety of ways,including those known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using rotary kilns. In the case of a rotarykiln, the material is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from 900° C. to1600° C., typically between 1200° C. to 1500° C. It is also within thescope of the present invention to perform some of the heat-treatment inbatches (e.g., for the nucleation step) and another continuously (e.g.,for the crystal growth step and to achieve the desired density). For thenucleation step, the temperature typically ranges between about 900° C.to about 1100° C., in some embodiments, preferably in a range from about925° C. to about 1050° C. Likewise for the density step, the temperaturetypically is in a range from about 1100° C. to about 1600° C., in someembodiments, preferably in a range from about 1200° C. to about 1500° C.This heat treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be feed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for, example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace. It is within the scope of the presentinvention to convert (e.g., crush) the resulting article or heat-treatedarticle to provide particles (e.g., abrasive particles).

[0097] The amorphous material is heat-treated to at least partiallycrystallize the amorphous material to provide glass-ceramic. Theheat-treatment of certain glasses to form glass-ceramics is well knownin the art. The heating conditions to nucleate and grow glass-ceramicsare known for a variety of glasses. Alternatively, one skilled in theart can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses according to the present invention, determine theappropriate nucleation and/or crystal growth conditions to provideglass-ceramics according to the present invention.

[0098] Typically, glass-ceramics are stronger than the amorphousmaterials from which they are formed. Hence, the strength of thematerial may be adjusted, for example, by the degree to which theamorphous material is converted to crystalline ceramic phase(s).Alternatively, or in addition, the strength of the material may also beaffected, for example, by the number of nucleation sites created, whichmay in turn be used to affect the number, and in turn the size of thecrystals of the crystalline phase(s). For additional details regardingforming glass-ceramics, see, for example Glass-Ceramics, P. W. McMillan,Academic Press, Inc., 2^(nd) edition, 1979, the disclosure of which isincorporated herein by reference.

[0099] For example, during heat-treatment of some exemplary amorphousmaterials for making glass-ceramics according to present invention,formation of phases such as La₂Zr₂O₇, and, if ZrO₂ is present,cubic/tetragonal ZrO₂, in some cases monoclinic ZrO₂, have been observedat temperatures above about 900° C. Although not wanting to be bound bytheory, it is believed that zirconia-related phases are the first phasesto nucleate from the amorphous material. Formation of Al₂O₃, ReAlO₃(wherein Re is at least one rare earth cation), ReAl₁₁O₁₈, Re₃Al₅O₁₂,Y₃Al₅O₁₂, etc. phases are believed to generally occur at temperaturesabove about 925° C. Typically, crystallite size during this nucleationstep is on order of nanometers. For example, crystals as small as 10-15nanometers have been observed. For at least some embodiments,heat-treatment at about 1300° C. for about 1 hour provides a fullcrystallization. In generally, heat-treatment times for each of thenucleation and crystal growth steps may range of a few seconds (in someembodiments even less than 5 seconds) to several minutes to an hour ormore.

[0100] Examples of crystalline phases which may be present in ceramicsaccording to the present invention include: complex Al₂O₃.metal oxide(s)(e.g., complex Al₂O₃.REO (e.g., ReAlO₃ (e.g., GdAlO₃ LaAlO₃), ReAl₁₁O₁₈(e.g., LaAl₁₁O₁₈,), and Re₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), complex Al₂O₃.Y₂O₃(e.g., Y₃Al₅O₁₂), and complex ZrO₂.REO (e.g., La₂Zr₂O₇)), Al₂O₃ (e.g.,α-Al₂O₃), and ZrO₂ (e.g., cubic ZrO₂ and tetragonal ZrO₂).

[0101] It is also with in the scope of the present invention tosubstitute a portion of the yttrium and/or aluminum cations in a complexAl₂O₃.metal oxide (e.g., complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminateexhibiting a garnet crystal structure)) with other cations. For example,a portion of the Al cations in a complex Al₂O₃.Y₂O₃ may be substitutedwith at least one cation of an element selected from the groupconsisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinations thereof.For example, a portion of the Y cations in a complex Al₂O₃.Y₂O₃ may besubstituted with at least one cation of an element selected from thegroup consisting of: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm,Yb, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof.Similarly, it is also with in the scope of the present invention tosubstitute a portion of the aluminum cations in alumina. For example,Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitute for aluminum in thealumina. The substitution of cations as described above may affect theproperties (e.g. hardness, toughness, strength, thermal conductivity,etc.) of the fused material.

[0102] It is also with in the scope of the present invention tosubstitute a portion of the rare earth and/or aluminum cations in acomplex Al₂O₃.metal oxide (e.g., complex Al₂O₃.REO) with other cations.For example, a portion of the Al cations in a complex Al₂O₃.REO may besubstituted with at least one cation of an element selected from thegroup consisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinationsthereof. For example, a portion of the Y cations in a complex Al₂O₃.REOmay be substituted with at least one cation of an element selected fromthe group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr,and combinations thereof. Similarly, it is also with in the scope of thepresent invention to substitute a portion of the aluminum cations inalumina. For example, Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitutefor aluminum in the alumina. The substitution of cations as describedabove may affect the properties (e.g. hardness, toughness, strength,thermal conductivity, etc.) of the fused material.

[0103] The average crystal size can be determined by the line interceptmethod according to the ASTM standard E 112-96 “Standard Test Methodsfor Determining Average Grain Size”. The sample is mounted in mountingresin (such as that obtained under the trade designation “TRANSOPTICPOWDER” from Buehler, Lake Bluff, Ill.) typically in a cylinder of resinabout 2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The mounted and polished sample issputtered with a thin layer of gold-palladium and viewed using ascanning electron microscopy (such as the JEOL SEM Model JSM 840A). Atypical back-scattered electron (BSE) micrograph of the microstructurefound in the sample is used to determine the average crystal size asfollows. The number of crystals that intersect per unit length (N_(L))of a random straight line drawn across the micrograph are counted. Theaverage crystal size is determined from this number using the followingequation.${{Average}\quad {Crystal}\quad {Size}} = \frac{1.5}{N_{L}M}$

[0104] Where N_(L) is the number of crystals intersected per unit lengthand M is the magnification of the micrograph. Ceramics (includingglass-ceramics) comprising abrasive particles according to the presentinvention comprise at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percentby volume crystallites, wherein the crystallites have an average size ofless than 1 micrometer. In another aspect, ceramics (includingglass-ceramics) comprising abrasive particles according to the presentinvention comprise less than at least 1, 2, 3, 5, 10, 15, 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100 percent by volume crystallites, wherein the crystallites have anaverage size of less than 0.5 micrometer. In another aspect, ceramics(including glass-ceramics) comprising abrasive particles according tothe present invention comprise less than at least 1, 2, 3, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume crystallites, wherein the crystalliteshave an average size of less than 0.3 micrometer. In another aspect,ceramics (including glass-ceramics) comprising abrasive particlesaccording to the present invention comprise less than at least 1, 2, 3,5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90,95, 97, 98, 99, or even 100 percent by volume crystallites, wherein thecrystallites have an average size of less than 0.15 micrometer.

[0105] Crystalline phases that may be present in ceramics according tothe present invention may include alumina (e.g., alpha and transitionaluminas), REO, HfO₂ ZrO₂, as well as, for example, one or more othermetal oxides such as BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO,NiO, Na₂O, P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, Y₂O₃, ZnO, “complexmetal oxides” (including “complex Al₂O₃.metal oxide (e.g., complexAl₂O₃.REO)), and combinations thereof.

[0106] Typically, and desirably, the (true) density, sometimes referredto as specific gravity, of ceramic according to the present invention istypically at least 70% of theoretical density. More desirably, the(true) density of ceramic according to the present invention is at least75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or 100% oftheoretical density.

[0107] Additional details regarding ceramics comprising Al₂O₃, at leastone of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, including making,using, and properties, can be found in application having U.S. Ser. Nos.09/922,526, 09/922,527, and 09/922,530, filed Aug. 2, 2001, and U.S.Ser. No. ______ (Attorney Docket Nos. 56931US005, 56931US006,56931US007, 56931US008, 56931US009, 56931US010, 57980US002, and57981US002, filed the same date as the instant application, thedisclosures of which are incorporated herein by reference.

[0108] Crystals formed by heat-treating amorphous to provide embodimentsof glass-ceramics according to the present invention may be, forexample, equiaxed, columnar, or flattened splat-like features.

[0109] Although an amorphous material, glass-ceramic, etc. according tothe present invention may be in the form of a bulk material, it is alsowithin the scope of the present invention to provide compositescomprising an amorphous material, glass-ceramic, etc. according to thepresent invention. Such a composite may comprise, for example, a phaseor fibers (continuous or discontinuous) or particles (includingwhiskers) (e.g., metal oxide particles, boride particles, carbideparticles, nitride particles, diamond particles, metallic particles,glass particles, and combinations thereof) dispersed in an amorphousmaterial, glass-ceramic, etc. according to the present invention,invention or a layered-composite structure (e.g., a gradient ofglass-ceramic to amorphous material used to make the glass-ceramicand/or layers of different compositions of glass-ceramics).

[0110] Abrasive particles according to the present invention generallycomprise crystalline ceramic (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume) crystallineceramic. In another aspect, the present invention provides a pluralityof particles having a particle size distribution ranging from fine tocoarse, wherein at least a portion of the plurality of particles areabrasive particles according to the present invention. In anotheraspect, embodiments of abrasive particles according to the presentinvention generally comprise (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, 99.9 or even 100 percent by volume)glass-ceramic.

[0111] The average hardness of the material of the present invention canbe determined as follows. Sections of the material are mounted inmounting resin (obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.) typically in a cylinder of resin about2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The microhardness measurements aremade using a conventional microhardness tester (such as that obtainedunder the trade designation “MITUTOYO MVK-VL” from Mitutoyo Corporation,Tokyo, Japan) fitted with a Vickers indenter using a 100-gram indentload. The microhardness measurements are made according to theguidelines stated in ASTM Test Method E384 Test Methods forMicrohardness of Materials (1991), the disclosure of which isincorporated herein by reference.

[0112] Abrasive particles according to the present invention can bescreened and graded using techniques well known in the art, includingthe use of industry recognized grading standards such as ANSI (AmericanNational Standard Institute), FEPA (Federation Europeenne des Fabricantsde Products Abrasifs), and JIS (Japanese Industrial Standard). Abrasiveparticles according to the present invention may be used in a wide rangeof particle sizes, typically ranging in size from about 0.1 to about5000 micrometers, more typically from about 1 to about 2000 micrometers;desirably from about 5 to about 1500 micrometers, more desirably fromabout 100 to about 1500 micrometers.

[0113] In a given particle size distribution, there will be a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards include those known as the American National StandardsInstitute, Inc. (ANSI) standards, Federation of European Producers ofAbrasive Products (FEPA) standards, and Japanese Industrial Standard(JIS) standards. ANSI grade designations (i.e., specified nominalgrades) include: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI 180,ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI600. Preferred ANSI grades comprising abrasive particles according tothe present invention are ANSI 8-220. FEPA grade designations includeP8, P12, P16, P24, P36, P40, P50, P60, P80, P100, P120, P150, P180,P220, P320, P400, P500, P600, P800, P1000, and P1200. Preferred FEPAgrades comprising abrasive particles according to the present inventionare P12-P220. JIS grade designations include JIS8, JIS12, JIS16, JIS24,JIS36, JIS46, JIS54, JIS60, JIS80, JIS100, JIS150, JIS180, JIS220,JIS240, JIS280, JIS320, JIS360, JIS400, JIS400, JIS600, JIS800, JIS1000,JIS1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS10,000. PreferredJIS grades comprising abrasive particles according to the presentinvention are JIS8-220.

[0114] After crushing and screening, there will typically be a multitudeof different abrasive particle size distributions or grades. Thesemultitudes of grades may not match a manufacturer's or supplier's needsat that particular time. To minimize inventory, it is possible torecycle the off demand grades back into melt to form glass. Thisrecycling may occur after the crushing step, where the particles are inlarge chunks or smaller pieces (sometimes referred to as “fines”) thathave not been screened to a particular distribution.

[0115] In another aspect, the present invention provides a method formaking abrasive particles, the method comprising heat-treating glassparticles according to the present invention to provide abrasiveparticles comprising a glass-ceramic according to the present invention.Alternatively, for example, the present invention provides a method formaking abrasive particles, the method comprising heat-treating glassaccording to the present invention, and crushing the resultingheat-treated material to provide abrasive particles comprising aglass-ceramic according to the present invention. When crushed, glasstends to provide sharper particles than crushing significantlycrystallized glass-ceramics or crystalline material.

[0116] In another aspect, the present invention provides agglomerateabrasive grains each comprised of a plurality of abrasive particlesaccording to the present invention bonded together via a binder. Inanother aspect, the present invention provides an abrasive article(e.g., coated abrasive articles, bonded abrasive articles (includingvitrified, resinoid, and metal bonded grinding wheels, cutoff wheels,mounted points, and honing stones), nonwoven abrasive articles, andabrasive brushes) comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles areabrasive particles (including where the abrasive particles areagglomerated) according to the present invention. Methods of making suchabrasive articles and using abrasive articles are well known to thoseskilled in the art. Furthermore, abrasive particles according to thepresent invention can be used in abrasive applications that utilizeabrasive particles, such as slurries of abrading compounds (e.g.,polishing compounds), milling media, shot blast media, vibratory millmedia, and the like.

[0117] Coated abrasive articles generally include a backing, abrasiveparticles, and at least one binder to hold the abrasive particles ontothe backing. The backing can be any suitable material, including cloth,polymeric film, fibre, nonwoven webs, paper, combinations thereof, andtreated versions thereof. The binder can be any suitable binder,including an inorganic or organic binder (including thermally curableresins and radiation curable resins). The abrasive particles can bepresent in one layer or in two layers of the coated abrasive article.

[0118] An example of a coated abrasive article is depicted in FIG. 1.Referring to this figure, coated abrasive article 1 has a backing(substrate) 2 and abrasive layer 3. Abrasive layer 3 includes abrasiveparticles according to the present invention 4 secured to a majorsurface of backing 2 by make coat 5 and size coat 6. In some instances,a supersize coat (not shown) is used.

[0119] Bonded abrasive articles typically include a shaped mass ofabrasive particles held together by an organic, metallic, or vitrifiedbinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel or cutoff wheel. The diameter of grindingwheels typically is about 1 cm to over 1 meter; the diameter of cut offwheels about 1 cm to over 80 cm (more typically 3 cm to about 50 cm).The cut off wheel thickness is typically about 0.5 mm to about 5 cm,more typically about 0.5 mm to about 2 cm. The shaped mass can also bein the form, for example, of a honing stone, segment, mounted point,disc (e.g. double disc grinder) or other conventional bonded abrasiveshape. Bonded abrasive articles typically comprise about 3-50% by volumebond material, about 30-90% by volume abrasive particles (or abrasiveparticle blends), up to 50% by volume additives (including grindingaids), and up to 70% by volume pores, based on the total volume of thebonded abrasive article.

[0120] A preferred form is a grinding wheel. Referring to FIG. 2,grinding wheel 10 is depicted, which includes abrasive particlesaccording to the present invention 11, molded in a wheel and mounted onhub 12.

[0121] Nonwoven abrasive articles typically include an open porous loftypolymer filament structure having abrasive particles according to thepresent invention distributed throughout the structure and adherentlybonded therein by an organic binder. Examples of filaments includepolyester fibers, polyamide fibers, and polyaramid fibers. In FIG. 3, aschematic depiction, enlarged about 100×, of a typical nonwoven abrasivearticle is provided. Such a nonwoven abrasive article comprises fibrousmat 50 as a substrate, onto which abrasive particles according to thepresent invention 52 are adhered by binder 54.

[0122] Useful abrasive brushes include those having a plurality ofbristles unitary with a backing (see, e.g., U.S. Pat. Nos. 5,427,595(Pihl et al.), 5,443,906 (Pihl et al.), 5,679,067 (Johnson et al.), and5,903,951 (Ionta et al.), the disclosure of which is incorporated hereinby reference). Desirably, such brushes are made by injection molding amixture of polymer and abrasive particles.

[0123] Suitable organic binders for making abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents(e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may thermally cured, radiation cured or combinations thereof.Additional details on binder chemistry may be found in U.S. Pat. Nos.4,588,419 (Caul et al.), 4,751,138 (Tumey et al.), and 5,436,063(Follett et al.), the disclosures of which are incorporated herein byreference.

[0124] More specifically with regard to vitrified bonded abrasives,vitreous bonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. In some cases, the vitreousbonding material includes crystalline phases. Bonded, vitrified abrasivearticles according to the present invention may be in the shape of awheel (including cut off wheels), honing stone, mounted pointed or otherconventional bonded abrasive shape. A preferred vitrified bondedabrasive article according to the present invention is a grinding wheel.

[0125] Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof, and the like. Typically, vitreous bondingmaterials can be formed from composition comprising from 10 to 100%glass frit, although more typically the composition comprises 20% to 80%glass frit, or 30% to 70% glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) ina range of about 700° C. to about 1500° C., usually in a range of about800° C. to about 1300° C., sometimes in a range of about 900° C. toabout 1200° C., or even in a range of about 950° C. to about 1100° C.The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry.

[0126] Preferred vitrified bonding materials may include thosecomprising silica, alumina (desirably, at least 10 percent by weightalumina), and boria (desirably, at least 10 percent by weight boria). Inmost cases the vitrified bonding material further comprise alkali metaloxide(s) (e.g., Na₂O and K₂O) (in some cases at least 10 percent byweight alkali metal oxide(s)).

[0127] Binder materials may also contain filler materials or grindingaids, typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for this invention include: metal carbonates (e.g., calciumcarbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g., talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

[0128] In general, the addition of a grinding aid increases the usefullife of the abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

[0129] Grinding aids encompass a wide variety of different materials andcan be inorganic or organic based. Examples of chemical groups ofgrinding aids include waxes, organic halide compounds, halide salts andmetals and their alloys. The organic halide compounds will typicallybreak down during abrading and release a halogen acid or a gaseoushalide compound. Examples of such materials include chlorinated waxeslike tetrachloronaphtalene, pentachloronaphthalene, and polyvinylchloride. Examples of halide salts include sodium chloride, potassiumcryolite, sodium cryolite, ammonium cryolite, potassiumtetrafluoroboate, sodium tetrafluoroborate, silicon fluorides, potassiumchloride, and magnesium chloride. Examples of metals include, tin, lead,bismuth, cobalt, antimony, cadmium, and iron titanium. Othermiscellaneous grinding aids include sulfur, organic sulfur compounds,graphite, and metallic sulfides. It is also within the scope of thepresent invention to use a combination of different grinding aids, andin some instances this may produce a synergistic effect. The preferredgrinding aid is cryolite; the most preferred grinding aid is potassiumtetrafluoroborate.

[0130] Grinding aids can be particularly useful in coated abrasive andbonded abrasive articles. In coated abrasive articles, grinding aid istypically used in the supersize coat, which is applied over the surfaceof the abrasive particles. Sometimes, however, the grinding aid is addedto the size coat. Typically, the amount of grinding aid incorporatedinto coated abrasive articles are about 50-300 g/m² (desirably, about80-160 g/m²). In vitrified bonded abrasive articles grinding aid istypically impregnated into the pores of the article.

[0131] The abrasive articles can contain 100% abrasive particlesaccording to the present invention, or blends of such abrasive particleswith other abrasive particles and/or diluent/particles. However, atleast about 2% by weight, desirably at least about 5% by weight, andmore desirably about 30-100% by weight, of the abrasive particles in theabrasive articles should be abrasive particles according to the presentinvention. In some instances, the abrasive particles according thepresent invention may be blended with another abrasive particles and/ordiluent particles at a ratio between 5 to 75% by weight, about 25 to 75%by weight about 40 to 60% by weight, or about 50% to 50% by weight(i.e., in equal amounts by weight). Examples of suitable conventionalabrasive particles include fused aluminum oxide (including white fusedalumina, heat-treated aluminum oxide and brown aluminum oxide), siliconcarbide, boron carbide, titanium carbide, diamond, cubic boron nitride,garnet, fused alumina-zirconia, and sol-gel-derived abrasive particles,and the like. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a rod or atriangle. Examples of sol gel abrasive particles include those describedU.S. Pat. Nos. 4,314,827 (Leitheiser et al.), 4,518,397 (Leitheiser etal.), 4,623,364 (Cottringer et al.), 4,744,802 (Schwabel), 4,770,671(Monroe et al.), 4,881,951 (Wood et al.), 5,011,508 (Wald et al.),5,090,968 (Pellow), 5,139,978 (Wood), 5,201,916 (Berg et al.), 5,227,104(Bauer), 5,366,523 (Rowenhorst et al.), 5,429,647 (Larmie), 5,498,269(Larmie), and 5,551,963 (Larmie), the disclosures of which areincorporated herein by reference. Additional details concerning sinteredalumina abrasive particles made by using alumina powders as a rawmaterial source can also be found, for example, in U.S. Pat. Nos.5,259,147 (Falz), 5,593,467 (Monroe), and 5,665,127 (Moltgen), thedisclosures of which are incorporated herein by reference. Additionaldetails concerning fused abrasive particles, can be found, for example,in U.S. Pat. Nos. 1,161,620 (Coulter), 1,192,709 (Tone), 1,247,337(Saunders et al.), 1,268,533 (Allen), and 2,424,645 (Baumann et al.)3,891,408 (Rowse et al.), 3,781,172 (Pett et al.), 3,893,826 (Quinan etal.), 4,126,429 (Watson), 4,457,767 (Poon et al.), 5,023,212 (Dubots et.al), 5,143,522 (Gibson et al.), and 5,336,280 (Dubots et. al), andapplications having U.S. Ser. Nos. 09,495,978, 09/496,422, 09/496,638,and 09/496,713, each filed on Feb. 2, 2000, and, Ser. Nos. 09/618,876,09/618,879, 09/619,106, 09/619,191, 09/619,192, 09/619,215, 09/619,289,09/619,563, 09/619,729, 09/619,744, and 09/620,262, each filed on Jul.19, 2000, and Ser. No. 09/772,730, filed Jan. 30, 2001, the disclosuresof which are incorporated herein by reference. In some instances, blendsof abrasive particles may result in an abrasive article that exhibitsimproved grinding performance in comparison with abrasive articlescomprising 100% of either type of abrasive particle.

[0132] If there is a blend of abrasive particles, the abrasive particletypes forming the blend may be of the same size. Alternatively, theabrasive particle types may be of different particle sizes. For example,the larger sized abrasive particles may be abrasive particles accordingto the present invention, with the smaller sized particles being anotherabrasive particle type. Conversely, for example, the smaller sizedabrasive particles may be abrasive particles according to the presentinvention, with the larger sized particles being another abrasiveparticle type.

[0133] Examples of suitable diluent particles include marble, gypsum,flint, silica, iron oxide, aluminum silicate, glass (including glassbubbles and glass beads), alumina bubbles, alumina beads and diluentagglomerates. Abrasive particles according to the present invention canalso be combined in or with abrasive agglomerates. Abrasive agglomerateparticles typically comprise a plurality of abrasive particles, abinder, and optional additives. The binder may be organic and/orinorganic. Abrasive agglomerates may be randomly shape or have apredetermined shape associated with them. The shape may be a block,cylinder, pyramid, coin, square, or the like. Abrasive agglomerateparticles typically have particle sizes ranging from about 100 to about5000 micrometers, typically about 250 to about 2500 micrometers.Additional details regarding abrasive agglomerate particles may befound, for example, in U.S. Pat. Nos. 4,311,489 (Kressner), 4,652,275(Bloecher et al.), 4,799,939 (Bloecher et al.), 5,549,962 (Holmes etal.), and 5,975,988 (Christianson), and applications having U.S. Ser.Nos. 09/688,444 and 09/688,484, filed Oct. 16, 2001, the disclosures ofwhich are incorporated herein by reference.

[0134] The abrasive particles may be uniformly distributed in theabrasive article or concentrated in selected areas or portions of theabrasive article. For example, in a coated abrasive, there may be twolayers of abrasive particles. The first layer comprises abrasiveparticles other than abrasive particles according to the presentinvention, and the second (outermost) layer comprises abrasive particlesaccording to the present invention. Likewise in a bonded abrasive, theremay be two distinct sections of the grinding wheel. The outermostsection may comprise abrasive particles according to the presentinvention, whereas the innermost section does not. Alternatively,abrasive particles according to the present invention may be uniformlydistributed throughout the bonded abrasive article.

[0135] Further details regarding coated abrasive articles can be found,for example, in U.S. Pat. Nos. 4,734,104 (Broberg), 4,737,163 (Larkey),5,203,884 (Buchanan et al.), 5,152,917 (Pieper et al.), 5,378,251(Culler et al.), 5,417,726 (Stout et al.), 5,436,063 (Follett et al.),5,496,386 (Broberg et al.), 5,609,706 (Benedict et al.), 5,520,711(Helmin), 5,954,844 (Law et al.), 5,961,674 (Gagliardi et al.), and5,975,988 (Christinason), the disclosures of which are incorporatedherein by reference. Further details regarding bonded abrasive articlescan be found, for example, in U.S. Pat. Nos. 4,543,107 (Rue), 4,741,743(Narayanan et al.), 4,800,685 (Haynes et al.), 4,898,597 (Hay et al.),4,997,461 (Markhoff-Matheny et al.), 5,037,453 (Narayanan et al.),5,110,332 (Narayanan et al.), and 5,863,308 (Qi et al.) the disclosuresof which are incorporated herein by reference. Further details regardingvitreous bonded abrasives can be found, for example, in U.S. Pat. Nos.4,543,107 (Rue), 4,898,597 (Hay et al.), 4,997,461 (Markhoff-Matheny etal.), 5,094,672 (Giles Jr. et al.), 5,118,326 (Sheldon et al.),5,131,926(Sheldon et al.), 5,203,886 (Sheldon et al.), 5,282,875 (Woodet al.), 5,738,696 (Wu et al.), and 5,863,308 (Qi), the disclosures ofwhich are incorporated herein by reference. Further details regardingnonwoven abrasive articles can be found, for example, in U.S. Pat. No.2,958,593 (Hoover et al.), the disclosure of which is incorporatedherein by reference.

[0136] The present invention provides a method of abrading a surface,the method comprising contacting at least one abrasive particleaccording to the present invention, with a surface of a workpiece; andmoving at least of one the abrasive particle or the contacted surface toabrade at least a portion of said surface with the abrasive particle.Methods for abrading with abrasive particles according to the presentinvention range of snagging (i.e., high pressure high stock removal) topolishing (e.g., polishing medical implants with coated abrasive belts),wherein the latter is typically done with finer grades (e.g., less ANSI220 and finer) of abrasive particles. The abrasive particle may also beused in precision abrading applications, such as grinding cam shaftswith vitrified bonded wheels. The size of the abrasive particles usedfor a particular abrading application will be apparent to those skilledin the art.

[0137] Abrading with abrasive particles according to the presentinvention may be done dry or wet. For wet abrading, the liquid may beintroduced supplied in the form of a light mist to complete flood.Examples of commonly used liquids include: water, water-soluble oil,organic lubricant, and emulsions. The liquid may serve to reduce theheat associated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

[0138] Abrasive particles according to the present invention may be usedto abrade workpieces such as aluminum metal, carbon steels, mild steels,tool steels, stainless steel, hardened steel, titanium, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

[0139] Abrasive particles according to the present invention may also beuseful, for example, as a filler/reinforcement material in composites(e.g., ceramic, metal, or polymeric (thermosetting or thermoplastic).The particles may, for example, increase the modulus, heat resistance,wear resistance, and/or strength of the matrix material. Although thesize, shape, and amount of the particles used to make a composite maydepend, for example, on the particular matrix material and use of thecomposite, the size of the reinforcing particles typically range about0.1 to 1500 micrometers, more typically 1 to 500 micrometers, anddesirably between 2 to 100 micrometers. The amount of particles forpolymeric applications is typically about 0.5 percent to about 75percent by weight, more typically about 1 to about 50 percent by weight.Examples of thermosetting polymers include: phenolic, melamine, ureaformaldehyde, acrylate, epoxy, urethane polymers, and the like. Examplesof thermoplastic polymers include: nylon, polyethylene, polypropylene,polyurethane, polyester, polyamides, and the like.

[0140] Examples of uses for reinforced polymeric materials (i.e.,abrasive particles according to the present invention dispersed in apolymer) include protective coatings, for example, for concrete,furniture, floors, roadways, wood, wood-like materials, ceramics, andthe like, as well as, anti-skid coatings and injection molded plasticparts and components.

[0141] Advantages and embodiments of this invention are furtherillustrated by the following examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this invention. Allparts and percentages are by weight unless otherwise indicated. Unlessotherwise stated, all examples contained no significant amount of SiO₂,B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅.

EXAMPLES Example 1

[0142] A polyethylene bottle was charged with 819.6 grams of aluminaparticles (obtained under the trade designation “APA-0.5” from CondeaVista, Tucson, Ariz.), 818 grams of lanthanum oxide particles (obtainedfrom Molycorp Inc.), 362.4 grams of yttria-stabilized zirconium oxideparticles obtained from Zirconia Sales, Inc. of Marietta, Ga. under thetrade designation “HSY-3”) and 1050 grams of distilled water. About 2000grams of the zirconia milling media (obtained from Tosoh Ceramics,Division of Bound Brook, N.J., under the trade designation “YTZ”) wereadded to the bottle, and the mixture was milled at 120 revolutions perminute (rpm) for 24 hours. After the milling, the milling media wereremoved and the slurry was poured onto a glass (“PYREX”) pan where itwas dried using a heat-gun. The dried mixture was ground with a mortarand pestle and screened through a 70-mesh screen (212-micrometer openingsize).

[0143] After grinding and screening, some of the particles were fed intoa hydrogen/oxygen torch flame. The torch used to melt the particles,thereby generating melted glass beads, was a Bethlehem bench burner PM2Dmodel B, obtained from Bethlehem Apparatus Co., Hellertown, Pa.,delivering hydrogen and oxygen at the following rates. For the innerring, the hydrogen flow rate was 8 standard liters per minute (SLPM) andthe oxygen flow rate was 3 SLPM. For the outer ring, the hydrogen flowrate was 23 (SLPM) and the oxygen flow rate was 9.8 SLPM. The dried andsized particles were fed directly into the torch flame, where they weremelted and transported to an inclined stainless steel surface(approximately 51 centimeters (cm) (20 inches) wide with the slope angleof 45 degrees) with cold water running over (approximately 8liters/minute) the surface to form beads.

Examples 2-25

[0144] Examples 2-25 beads were prepared as described in Example 1,except the raw materials and the amounts of raw materials, used arelisted in Table 1, below, and the milling of the raw materials wascarried out in 90 milliliters (ml) of isopropyl alcohol with 200 gramsof the zirconia media (obtained from Tosoh Ceramics, Division of BoundBrook, N.J., under the trade designation “YTZ”) at 120 rpm for 24 hours.The sources of the raw materials used are listed in Table 2, below.TABLE 1 Example Weight percent of components Batch amounts, g  2* La₂O₃48 La₂O₃ 240 Al₂O₃ 52 Al₂O₃: 260  3 La₂O₃: 43 La₂O₃:  21.5 Al₂O₃: 32Al₂O₃:  16 ZrO₂: 12 ZrO₂:   6 SiO₂: 13 SiO₂:   6.5  4 La₂O₃: 45.06La₂O₃:  22.53 Al₂O₃: 34.98 Al₂O₃:  17.49 ZrO₂: 19.96 ZrO₂:   9.98  5La₂O₃: 38.65 La₂O₃:  19.33 Al₂O₃: 38.73 Al₂O₃:  19.37 ZrO₂: 22.62 ZrO₂: 11.31  6 La₂O₃: 32.58 La₂O₃:  16.2 Al₂O₃: 52.98 Al₂O₃:  26.49 ZrO₂:14.44 ZrO₂:   7.22  7 CeO₂: 41.4 CeO₂:  20.7 Al₂O₃: 40.6 Al₂O₃:  20.3ZrO₂: 18 ZrO₂:   9.00  8 Al₂O₃: 41.0 Al₂O₃:  20.5 ZrO₂: 18.0 ZrO₂:   9.0Gd₂O₃: 41.0 Gd₂O₃:  20.5  9 Al₂O₃: 40.9 Al₂O₃:  20.45 Er₂O₃: 40.9 Er₂O₃: 20.45 ZrO₂: 18.2 ZrO₂:   9.1 10 La₂O₃: 35.0 La₂O₃:  17.5 Al₂O₃: 40.98Al₂O₃:  20.49 ZrO₂: 18.12 ZrO₂:   9.06 Nd₂O₃:  5.0 Nd₂O₃:   2.50 11La₂O₃: 35.0 La₂O₃:  17.5 Al₂O₃: 40.98 Al₂O₃:  20.49 ZrO₂: 18.12 ZrO₂:  9.06 CeO₂:  5.0 CeO₂:   2.50 12 HfO₂: 35.5 HfO₂:  17.75 Al₂O₃: 32.5Al₂O₃:  16.25 La₂O₃: 32.5 La₂O₃:  16.25 13 La₂O₃: 41.7 La₂O₃:  20.85Al₂O₃: 35.4 Al₂O₃:  17.7 ZrO₂: 16.9 ZrO₂:   8.45 MgO:  6.0 MgO:   3.0 14La₂O₃: 43.02 La₂O₃:  21.51 Al₂O₃: 36.5 Al₂O₃:  18.25 ZrO₂: 17.46 ZrO₂:  8.73 Li₂CO₃:  3.0 Li₂CO₃:   1.50 15 La₂O₃: 38.8 La₂O₃:  19.4 Al₂O₃:40.7 Al₂O₃:  20.35 ZrO₂: 17.5 ZrO₂:   8.75 Li₂CO₃:  6 Li₂CO₃   3 16La₂O₃: 43.02 La₂O₃:  21.51 Al₂O₃: 36.5 Al₂O₃:  18.25 ZrO₂: 17.46 ZrO₂:  8.73 TiO₂: 3% TiO₂:   1.50 17 Y₂O₃: 45.06 La₂O₃:  14.35 Al₂O₃: 34.98Al₂O₃:  26.35 ZrO₂: 19.96 ZrO₂:   9.3 18 Y₂O₃: 27.6 La₂O₃:  13.8 Al₂O₃:57.5 Al₂O₃:  23.75 ZrO₂: 14.9 ZrO₂:   7.45 19 Y₂O₃: 27.44 La₂O₃:  13.72Al₂O₃: 57.14 Al₂O₃:  28.57 ZrO₂: 15.43 ZrO₂:   7.71 20 Y₂O₃: 28.7 La₂O₃: 14.35 Al₂O₃: 55.7 Al₂O₃:  27.85 ZrO₂: 15.5 ZrO₂:   7.75 21 Y₂O₃: 19Y₂O₃:   9.5 Al₂O₃: 51 Al₂O₃:  25.5 ZrO₂: 17.9 ZrO₂:   8.95 La₂O₃: 12.1La₂O₃:   6.05 22 Y₂O₃: 19.3 Y₂O₃:   9.65 Al₂O₃: 50.5 Al₂O₃:  25.25 ZrO₂:17.8 ZrO₂:   8.9 Nd₂O₃: 12.4 Nd₂O₃:   6.2 23 Y₂O₃: 27.4 Y₂O₃:  13.7Al₂O₃: 50.3 Al₂O₃:  25.15 ZrO₂: 17.8 ZrO₂:   8.9 Li₂CO₃:  4.5 Li₂CO₃:  2.25 24 HfO₂: 20.08 HfO₂:  14.04 Al₂O₃: 46.55 Al₂O₃:  23.27 Y₂O₃:25.37 Y₂O₃:  12.67 25 Y₂O₃: 27.4 Y₂O₃:  13.7 Al₂O₃: 50.3 Al₂O₃:  25.15ZrO₂: 17.8 ZrO₂:   8.9 MgO:  4.5 MgO:   2.25

[0145] TABLE 2 Raw Material Source Alumina particles Obtained fromCondea Vista, (Al₂O₃) Tucson, AZ under the trade designation “APA-0.5”Calcium oxide particles Obtained from Alfa Aesar, (CaO) Ward Hill, MACerium oxide particles Obtained from Rhone-Poulenc, (CeO₂) France Erbiumoxide particles Obtained from Aldrich (Er₂O₃) Chemical Co., Milwaukee,WI Gadolinium oxide Obtained from Molycorp Inc., particles (Gd₂O₃)Mountain Pass, CA Hafnium oxide particles Obtained from Teledyne Wah(HfO₂) Chang Albany Company, Albany, OR Lanthanum oxide Obtained fromMolycorp Inc., particles (La₂O₃) Mountain Pass, CA Lithium carbonateObtained from Aldrich particles (Li₂CO₃) Chemical Co. Magnesium oxideObtained from Aldrich particles (MgO) Chemical Co. Neodymium oxidObtained from Molycorp Inc. particles (Nd₂O₃) Silica particles (SiO₂)Obtained from Alfa Aesar, Ward Hill, MA Sodium bicarbonate Obtained fromAldrich particles (NaHCO₃) Chemical Co. Titanium dioxide Obtained fromKemira Inc., particles (TiO₂) Savannah, GA Yttria-stabilized Obtainedfrom Zirconia Sales, zirconium oxide Inc. of Marietta, GA underparticles (Y-PSZ) the trade designation “HSY-3” Yttrium oxide particlesObtained from H. C. Stark (Y₂O₃) Newton, MA

[0146] Various properties/characteristics of some Example 1-25 materialwere measured as follows. Powder X-ray diffraction (using an X-raydiffractometer (obtained under the trade designation “PHILLIPS XRG 3100”from PHILLIPS, Mahwah, N.J.) with copper K α1 radiation of 1.54050Angstrom)) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the amorphous nature of a material. The existence ofboth a broad peak and well-defined peaks was taken as an indication ofthe existence of crystalline matter within an amorphous matrix. Phasesdetected in various examples are reported in Table 3, below. TABLE 3Phases detected Hot- via X-ray pressing Example diffraction ColorT_(g),° C. T_(x), ° C. temp, ° C. 1 Amorphous* Clear 834 937 960 2Amorphous* Clear 840 925 960 3 Amorphous* Clear 837 1001 — 4 Amorphous*Clear 837 936 — 5 Amorphous* Clear 850 923 — 6 Amorphous* Clear/ 858 914965 and milky Crystalline 7 Amorphous* Brown 838 908 960 and Crystalline8 Amorphous* Clear 886 933 985 9 Amorphous* Intense pink 858 914 — 10Amorphous* Blue/ 836 930 965 purple 11 Amorphous* Yellow 831 934 965 12Amorphous* Clear/ 828 937 960 greenish 13 Amorphous* Clear 795 901 95014 Amorphous* Clear 816 942 950 15 Amorphous* Clear 808 940 950 16Amorphous* Clear/ 834 935 950 Greenish 17 Amorphous* Clear/ 865 941 980and milky Crystalline 18 Amorphous* Clear/ 871 934 — and milkyCrystalline 19 Amorphous* Clear/ 874 937 — and milky Crystalline 20Amorphous* Clear/ 870 942 — and milky Crystalline 21 Amorphous* Clear843 938 970 22 Amorphous* Blue/ 848 934 970 pink 23 Amorphous* Clear 852941 970 24 Amorphous* Clear/ 867 948 — and Greenish Crystalline 25Amorphous* Clear/ 869 934 — and milky Crystalline

[0147] For differential thermal analysis (DTA), a material was screenedto retain beads in the 90-125 micrometer size range. DTA runs were made(using an instrument obtained from Netzsch Instruments, Selb, Germanyunder the trade designation “NETZSCH STA 409 DTA/TGA”). The amount ofeach screened sample placed in a 100-microliter Al₂O₃ sample holder was400 milligrams. Each sample was heated in static air at a rate of 10°C./minute from room temperature (about 25° C.) to 1200° C.

[0148] Referring to FIG. 4, line 123 is the plotted DTA data for theExample 1 material. Referring to FIG. 4 line 123, the material exhibitedan endothermic event at a temperature around 834° C., as evidenced bythe downward curve of line 123. It was believed that this event was dueto the glass transition (T_(g)) of the glass material. At about 937° C.,an exothermic event was observed as evidenced by the sharp peak in line123. It was believed that this event was due to the crystallization(T_(x)) of the material. These T_(g) and T_(x) values for other examplesare reported in Table 3, above.

[0149] For each of Examples 1-25, about 25 grams of the beads wereplaced in a graphite die and hot-pressed using uniaxial pressingapparatus (obtained under the trade designation “HP-50”, ThermalTechnology Inc., Brea, Calif.). The hot-pressing was carried out in anargon atmosphere and 13.8 megapascals (MPa) (2000 pounds per square inch(2 ksi)) pressure. The hot-pressing temperature at which appreciableglass flow occurred, as indicated by the displacement control unit ofthe hot pressing equipment described above, is reported for variousexamples in Table 3, above. About 400 grams of Example 1 beads and 200grams of Example 2 beads were hot-pressed.

[0150] Example 1-25 beads were heat-treated in a furnace (anelectrically heated furnace (obtained under the trade designation “ModelKKSK-666-3100” from Keith Furnaces of Pico Rivera, Calif.)) as follows.The beads were heated from room temperature (about 25° C.) to about1300° C. at a rate of about 10° C./minute and then held at 1300° C. forabout 1 hour before cooling back to room temperature by turning off thefurnace.

[0151] FIGS. 5-9 are scanning electron microscope (SEM) photomicrographsof a polished section of heat-treated Examples 2, 6, 7, 8, and 17materials, respectively. The polished sections were prepared usingconventional mounting and polishing techniques. Polishing was done usinga polisher (obtained from Buehler of Lake Bluff, Ill. under the tradedesignation “ECOMET 3 TYPE POLISHER-GRINDER”). The sample was polishedfor about 3 minutes with a diamond wheel, followed by three minutes ofpolishing with each of 45, 30, 15, 9, and 3-micrometer diamond slurries.The polished sample was sputter coated with a thin layer ofgold-palladium and viewed using JEOL SEM (Model JSM 840A).

[0152] Phases present after heat-treatment were analyzed using powderX-ray diffraction techniques as described above. The results aresummarized in Table 4, below. TABLE 4 Phases detected via X-ray Examplediffraction Hardness, GPa 1 Cubic/tetragonal ZrO₂ 16.4 ± 0.3 α-Al₂O₃LaAl₁₁O₁₈ LaAlO₃ 2 LaAl₁₁O₁₈ 16.0 ± 0.4 LaAlO₃ 6 Cubic/tetragonal ZrO₂16.7 ± 0.2 α-Al₂O₃ LaAl₁₁O₁₈ LaAlO₃ 8 Cubic/tetragonal ZrO₂ 16.9 ± 0.1GdAlO₃ α-Al₂O₃ 17 Cubic/tetragonal ZrO₂ 17.4 ± 0.4 Y₃Al₅O₁₂ α-Al₂O₃ 21Cubic/tetragonal ZrO₂ Y₃Al₅O₁₂ LaAlO₃ α-Al₂O₃ 23 Cubic/tetragonal ZrO₂16.9 ± 0.3 Y₃Al₅O₁₂ α-Al₂O₃

[0153] The average microhardnesses of heat-treated beads from selectedExamples were measured by mounting loose beads (about 125 micrometers insize) in mounting resin (obtained under the trade designation “EPOMET”from Buehler Ltd., Lake Bluff, Ill.). The resulting cylinder of resinwas about 2.5 cm (1 inch) in diameter and about 1.9 cm (0.75 inch) high.The mounted samples were polished using a conventional grinder/polisher(obtained under the trade designation “EPOMET” from Buehler Ltd.) andconventional diamond slurries with the final polishing step using a1-micrometer diamond slurry (obtained under the trade designation“METADI” from Buehler Ltd.) to obtain polished cross-sections of thesample.

[0154] The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness values werean average of 20 measurements. The average microhardness values arereported in Table 4, above.

Grinding Performance of Examples 1, 1A, and 2 and Comparative ExamplesA-C

[0155] Examples 1 and 2 hot-pressed material was crushed by using a“Chipmunk” jaw crusher (Type VD, manufactured by BICO Inc., Burbank,Calif.) into (abrasive) particles and graded to retain the −25+30 meshfraction (i.e., the fraction collected between 25-micrometer openingsize and 30-micrometer opening size sieves) and −30+35 mesh fractions(i.e., the fraction collected between 30-micrometer opening size and35-micrometer opening size sieves) (USA Standard Testing Sieves). Thesetwo mesh fractions were combined to provide a {fraction (50/50)} blend.The blended material was heat treated at 1300° C. for 1 hour asdescribed above. Thirty grams of the resulting glass-ceramic abrasiveparticles were incorporated into a coated abrasive disc. The coatedabrasive disc was made according to conventional procedures. Theglass-ceramic abrasive particles were bonded to 17.8 cm diameter, 0.8 mmthick vulcanized fiber backings (having a 2.2 cm diameter center hole)using a conventional calcium carbonate-filled phenolic make resin (48%resole phenolic resin, 52% calcium carbonate, diluted to 81% solids withwater and glycol ether) and a conventional cryolite-filled phenolic sizeresin (32% resole phenolic resin, 2% iron oxide, 66% cryolite, dilutedto 78% solids with water and glycol ether). The wet make resin weightwas about 185 g/m². Immediately after the make coat was applied, theglass-ceramic abrasive particles were electrostatically coated. The makeresin was precured for 120 minutes at 88° C. Then the cryolite-filledphenolic size coat was coated over the make coat and abrasive particles.The wet size weight was about 850 grams per square (g/m²). The sizeresin was cured for 12 hours at 99° C. The coated abrasive discs wereflexed prior to testing.

[0156] Example 1A coated abrasive disk was prepared as described forExample 1 except the Example 1A abrasive particles were obtained bycrushing a hot-pressed and heat-treated Example 1 material, rather thancrushing then heat-treating.

[0157] Comparative Example A coated abrasive discs were prepared asdescribed for Example 6 (above), except heat-treated fused aluminaabrasive particles (obtained under the trade designation “ALODUR BFRPL”from Triebacher, Villach, Austria) was used in place of the Example 1glass-ceramic abrasive particles.

[0158] Comparative Example B coated abrasive discs were prepared asdescribed for Example 6 (above), except alumina-zirconia abrasiveparticles (having a eutectic composition of 53% Al₂O₃ and 47% ZrO₂;obtained under the trade designation “NORZON” from Norton Company,Worcester, Mass.) were used in place of the Example 1 glass-ceramicabrasive particles.

[0159] Comparative Example C coated abrasive discs were prepared asdescribed above except sol-gel-derived abrasive particles (marketedunder the trade designation “321 CUBITRON” from the 3M Company, St.Paul, Minn.) were used in place of the Example 1 glass-ceramic abrasiveparticles.

[0160] The grinding performance of Examples 1, 1A, 2, and ComparativeExamples A-C coated abrasive discs were evaluated as follows. Eachcoated abrasive disc was mounted on a beveled aluminum back-up pad, andused to grind the face of a pre-weighed 1.25 cm×18 cm×10 cm 1018 mildsteel workpiece. The disc was driven at 5,000 rpm while the portion ofthe disc overlaying the beveled edge of the back-up pad contacted theworkpiece at a load of 8.6 kilograms. Each disc was used to grind anindividual workpiece in sequence for one-minute intervals. The total cutwas the sum of the amount of material removed from the workpiecesthroughout the test period. The total cut by each sample after 12minutes of grinding as well as the cut at the 12th minute (i.e., thefinal cut) are reported in Table 6, below. The Example 1 results are anaverage of two discs, where as one disk was tested for each of Example1A and Comparative Examples A, B, and C. TABLE 6 Example Total cut, gFinal cut, g 1 1163 91 1 A 1197 92 2 1094 91 Comp. A 514 28 Comp. B 68953 Comp. C 1067 89

[0161] Various modifications and alterations of this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein at least 80 percent by weight of the glass-ceramic collectively comprises the Al₂O₃ and REO, based on the total weight of the glass-ceramic.
 2. The abrasive particle according to claim 1 comprising at least 90 percent by volume of said glass-ceramic, based on the total volume of said abrasive particle.
 3. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass-ceramic collectively comprises the Al₂O₃ and REO, and less than 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based on the total weight of the glass-ceramic.
 4. The abrasive particle according to claim 3 comprising at least 90 percent by volume of said glass-ceramic, based on the total volume of said abrasive particle.
 5. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass-ceramic collectively comprises the Al₂O₃ and REO, and less than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass-ceramic.
 6. The abrasive particle according to claim 5 comprising at least 90 percent by volume of said glass-ceramic, based on the total volume of said abrasive particle.
 7. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein the ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 1 micrometer, and (b) is free of eutectic microstructure features.
 8. The abrasive particle according to claim 7 comprising at least 90 percent by volume of said glass-ceramic, based on the total volume of said abrasive particle.
 9. A method for making abrasive particles, the method comprising: heat-treating glass particles comprising Al₂O₃ and REO, wherein at least 80 percent by weight of the glass collectively comprises the Al₂O₃ and REO, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 10. A method for making abrasive particles, the method comprising: heat-treating particles comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 80 percent by weight of the glass collectively comprises the Al₂O₃ and REO, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 11. A method for making abrasive particles, the method comprising: heat-treating glass comprising Al₂O₃ and REO, wherein at least 80 percent by weight of the glass collectively comprises the Al₂O₃ and REO, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 12. A method for making abrasive particles, the method comprising: heat-treating ceramic comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 80 percent by weight of the glass collectively comprises the Al₂O₃ and REO, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 13. A method for making abrasive particles, the method comprising: heat-treating glass particles comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 14. A method for making abrasive particles, the method comprising: heat-treating particles comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 15. A method for making abrasive particles, the method comprising: heat-treating glass comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 16. A method for making abrasive particles, the method comprising: heat-treating ceramic comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 17. A method for making abrasive particles, the method comprising: heat-treating glass particles comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 18. A method for making abrasive particles, the method comprising: heat-treating particles comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass particles, to provide glass-ceramic abrasive particles.
 19. A method for making abrasive particles, the method comprising: heat-treating glass comprising Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 20. A method for making abrasive particles, the method comprising: heat-treating ceramic comprising glass, wherein the glass comprises Al₂O₃ and REO, wherein at least 60 percent by weight of the glass collectively comprises the Al₂O₃ and REO, and less than 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of the glass, to provide glass-ceramic; and converting the glass-ceramic to provide abrasive particles.
 21. A method for making abrasive particles, the method comprising: heat-treating glass particles comprising Al₂O₃ and REO to provide glass-ceramic abrasive particles, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 1 micrometer, and (b) is free of eutectic microstructure features.
 22. A method for making abrasive particles, the method comprising: heat-treating particles comprising glass, wherein the glass comprises Al₂O₃ and REO to provide glass-ceramic abrasive particles, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 1 micrometer, and (b) is free of eutectic microstructure features.
 23. A method for making abrasive particles, the method comprising: heat-treating glass comprising Al₂O₃ and REO to provide glass-ceramic, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 1 micrometer, and (b) is free of eutectic microstructure features; and converting the glass-ceramic to provide abrasive particles.
 24. A method for making abrasive particles, the method comprising: heat-treating ceramic comprising glass, wherein the glass comprises Al₂O₃ and REO to provide glass-ceramic, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 1 micrometer, and (b) is free of eutectic microstructure features; and converting the glass-ceramic to provide abrasive particles.
 25. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 200 nanometers and (b) has a density of at least 90% of theoretical density.
 26. The abrasive particle according to claim 25 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 27. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites, wherein none of the crystallites are greater than 200 nanometers in size and (b) has a density of at least 90% of theoretical density.
 28. The abrasive particle according to claim 27 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 29. Abrasive particle comprising a glass-ceramic comprising Al₂O₃ and REO, wherein the glass-ceramic (a) exhibits a microstructure comprising crystallites, wherein at least a portion of the crystallites are not greater than 150 nanometers in size and (b) has a density of at least 90% of theoretical density.
 30. The abrasive particle according to claim 29 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 31. Abrasive particle comprising ceramic comprising at least 75 percent by volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃ and REO, wherein the ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size of less than 200 nanometers and (b) has a density of at least 90% of theoretical density.
 32. The abrasive particle according to claim 31 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 33. Abrasive particle comprising ceramic comprising at least 75 percent by volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃ and REO, wherein the ceramic (a) exhibits a microstructure comprising crystallites, wherein none of the crystallites are greater than 200 nanometers in size and (b) has a density of at least 90% of theoretical density.
 34. The abrasive particle according to claim 33 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 35. Abrasive particle comprising ceramic comprising at least 75 percent by volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃ and REO, wherein the ceramic (a) exhibits a microstructure comprising crystallites, wherein at least a portion of the crystallites are not greater than 150 nanometers in size and (b) has a density of at least 90% of theoretical density.
 36. The abrasive particle according to claim 35 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle.
 37. Abrasive particle comprising ceramic comprising at least 75 percent by volume crystalline ceramic, the crystalline ceramic comprising Al₂O₃ and REO, wherein the ceramic (a) exhibits a microstructure comprising crystallites having an average crystallite size not greater than 200 nanometer, in size and (b) has a density of at least 90% of theoretical density.
 38. The abrasive particle according to claim 37 comprising at least 90 percent by volume of said ceramic, based on the total volume of said abrasive particle. 